The invention relates to sulfur-curable rubber skim stocks containing dithiodipropionic acid. More particularly, the invention relates to sulfur-curable rubber skim stocks which contain dithiodipropionic acid as a co-curing agent with sulfur.
Sulfur-curable rubber skim stocks especially those containing relatively high levels of sulfur are susceptible to sulfur blooming under common storage conditions. Stocks containing sulfur bloom often lack building tack which can lead to poor adhesion properties. Accordingly, it is generally necessary to remove the sulfur bloom from the surface of the stock using an organic solvent prior to using the stock to form laminates. As will be evident, this can be a time consuming procedure and in addition the use of organic solvents for such a purpose often leads to the emission of solvent fumes to the ambient atmosphere. Thus, it is conventional practice to replace a portion of the elemental sulfur in such rubber skim stocks with a so-called sulfur donor compound. Such sulfur donor compounds are materials which liberate sulfur during the curing process. However, it has been found that many conventionally used sulfur donor compounds cause a detrimental effect on the adhesion of the cured skim stock to brass-plated steel, particularly adhesion of the cured skim stock to brass-plated steel under high humidity, heat aging conditions. Thus, the discovery of a sulfur donor compound which does not cause a detrimental effect on the adhesion of the rubber skim stock to brass-plated steel under high humidity, heat aging conditions would constitute an important development.